In recent years, in an automatic transmission that is mounted in a vehicle or the like, multi-speed shifting is coming to play a central role in satisfying the need to improve fuel economy and the like. Such an automatic transmission is disclosed, for example, in Japanese Patent Application Publication No. JP-A-2001-182785 (in particular, refer to FIG. 2 and TABLE 2).
The automatic transmission disclosed in JP-A-2001-182785 is provided with a speed reduction planetary gear set (G1) that receives the input rotation that is input to an input shaft (11) and reduces the speed of that rotation, first and second input transfer clutches (C4, C3) that selectively transfers the input rotation, first and second reduced speed transfer clutches (C2, C1) that selectively transfers rotation at a speed reduced through the speed reduction planetary gear set (G1), first and second brakes (B1, B2), that brake the rotation on the case (1), and a planetary gear set (G23) that has at least first, second, third, and fourth rotary elements (S2, S3, PC2 and PC3, R3). This automatic transmission inputs rotation through the first input transfer clutch (C4) to the first rotary element (S2) of the planetary gear set (G23) and the reduced speed rotation is output through the first speed reduction transfer clutch (C2) while the first rotary element (S2) is held stationary on the case (1) by the first brake (B1). The automatic transmission is structured such that reduced speed rotation can be transferred to the second rotary element (S3) by the second speed reduction transfer clutch (C1). Further, input rotation can be transferred through the second input transfer clutch (C3) to the third rotary element combination of (PC2 and PC3) and the third rotary element can be held stationary by the second brake (B2). Rotation can be output from the fourth rotary element (R2, R3). Thus, by appropriately operating these clutches (C1, C2, C3, C4) and brakes (B1, B2), the automatic transmission enables multi-speed shifting.
However, as shown in TABLE 2 of JP-A-2001-182780, while the first forward speed to the eighth forward speed can be established by suitably operating the clutches and brakes, the third rotary elements (PC2 and PC3), which receive the input rotation by engagement of the second input transfer clutch (C3), do not attain a speed that is higher than the input rotation, even if the first rotary element (S2) receives input rotation by engagement of the first input transfer clutch (C4), because, for example, in the fifth forward speed, the first input transfer clutch (C4) is released, a reduced speed rotation is input to the second rotary element (S3) by engagement of the first speed reduction transfer clutch (C1), and rotation is input to the third rotary element (PC2 and PC3) by engagement of the second input transfer clutch (C3), resulting in a high speed rotation, that is, a speed that is higher than that of the input rotation.